1. Field of the Invention
The present invention relates to a work conveyor sprocket and link assembly adapted for use in an abrasive environment and, more particularly, to a sprocket and link assembly having increased wear resistance capabilities arising from a configuration which distributes applied forces over a relatively large surface area.
2. Description of the Prior Art
Sprocket and link assemblies typically have a pin and roller arrangement, the rollers being engageable between radially exending teeth of the sprocket. Upon rotation of the sprocket, the teeth of the sprocket apply a force to the rollers and thereby drive the link assembly. In turn, the link assembly can cause the rotation of other sprockets, gears or any suitably configured apparatus which has teeth or some similar force-receiving means to which the now-driven link assembly is engaged. Alternatively, the link assembly can be driven in some manner so that the sprocket is rotated by the link assembly.
Whether the sprocket is the driving member or is itself driven, and whether the product runs in a forward or reverse direction, the sprocket teeth are the conduit for the transmission of force. The teeth typically are small relative to the overall size of the sprocket. Consequently, the amount of applied force can be large in relation to the relatively small surface area provided by the teeth, resulting in high stress concentrations. The resultant highly localized force can cause excessive wear and failure of the sprocket teeth.
The problem of stress concentrations is aggravated when a sprocket and link assembly is used in an abrasive environment. Lubricants, such as oil and the like, cannot be used effectively because lubricants tend to collect and hold abrasive materials in the vicinity of the intermeshing parts. Due to the presence of abrasive materials, excessive wear of the links and the sprocket teeth can occur.
There have been attempts to overcome the various problems associated with sprocket and link assemblies. U.S. Pat. No. 1,218,368 discloses an apparatus for preventing pivots of a drive chain from being forced too deeply into the spaces between the teeth of a sprocket. This reference states that permitting the pivots to deeply engage the spaces between the teeth unnecessarily consumes the transferable driving power and produces an accelerated wear of the working parts. Consequently, circular rims were provided on either side of the teeth to prevent the pivots from entering too deeply into the spaces between the teeth. Unfortunately, this design actually provides less surface area to transmit the applied force because the rims restrict the links to applying the transferred force along a higher, and consequently smaller, portion of the teeth.
U.S. Pat. No. 4,072,062 discloses a self-cleaning sprocket. The sprocket includes teeth-like projections extending outwardly on each side of a sprocket having a smooth-surfaced, disc-like center portion. An elastomeric endless belt having lugs engageable with the teeth is entrained about the sprocket. The combination of the sprocket configuration and the lugs enables the sprocket to be self-cleaning. The desirability of increasing the contact surface area between the lugs and the sprocket is not addressed.
Another sprocket and link assembly especially adapted for use as part of a conveyor in an abrasive environment has been developed by the Pangborn Company of Hagerstown, Md., Model 6GO-3. In this sprocket and link assembly, the sprocket includes eight radially extending teeth connected by flat-bottomed root portions. The sprocket includes a bore through its center with the sprocket being split along the centerline of the bore so that the sprocket can be easily attached to, and removed from, a drive shaft. Sixteen shoulder portions extend outwardly of the sprocket on each side. The shoulder portions extend along the base of the teeth. The links include laterally extending tangs to which slats are secured. The slats cooperate to define a conveyor for supporting workpieces. The links engage the teeth near the flat-bottomed root portions; the links also engage the shoulder portions. Because both the teeth and the shoulder portions are in driving engagement with the links, stress concentrations are reduced. The decrease in stress concentration is sufficiently great that acceptable results have been produced in an abrasive environment.
Although the Model 6GO-3 sprocket and link assembly generally has been satisfactory, certain concerns have not been addressed. One concern relates to the possibility of further increasing the available contact area between the sprocket and the links. An additional concern relates to the manufacturing costs associated with machining shoulder portions on the sprocket. Other concerns relate to the links, particularly to the effort needed to assemble and disassemble the links. The links in the Model 6GO-3 sprocket and link assembly are held together by link pins which themselves are held in place by relatively inaccessible roll pins. Another concern related to the links is the manner in which workpieces are carried by the conveyor. in the Model 6GO-3 sprocket and link assembly, the slats are connected to the links in such a manner that a relatively wide slat gap exists. It would be desirable to provide a conveyor having a reduced slat-to-slat gap.